Difference between revisions of "Flow in a swale"
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[[File:Swale_sections.PNG| | {{float right|[[File:Swale_sections.PNG|frameless|450 px]]}} | ||
Flow (''Q'') in an open channel, such as a [[swale]], may be calculated using Manning's equation: | Flow (''Q'') in an open channel, such as a [[swale]], may be calculated using Manning's equation: | ||
<math>Q=VA=\frac{R^{\frac{2}{3}}S^{\frac{1}{2}}}{n}</math> | <math>Q=VA=\frac{R^{\frac{2}{3}}S^{\frac{1}{2}}}{n}</math> | ||
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*''P'' = the wetted perimeter of the swale (m) | *''P'' = the wetted perimeter of the swale (m) | ||
*''S'' = the longitudinal slope (m/m) | *''S'' = the longitudinal slope (m/m) | ||
*''n'' = [[Manning's coefficient]] (dimensionless)}} | *''n'' = [[Manning's coefficient]] or 'Manning's n' (dimensionless)}} | ||
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{{:Manning's n}} | |||
Latest revision as of 13:07, 4 July 2019
Flow (Q) in an open channel, such as a swale, may be calculated using Manning's equation:
Where:
Where:
- Q = the flow in the swale (m3/s)
- A = the cross sectional area of the swale (m2)
- P = the wetted perimeter of the swale (m)
- S = the longitudinal slope (m/m)
- n = Manning's coefficient or 'Manning's n' (dimensionless)
| n value range | Good condition turf grass | Other |
|---|---|---|
| 0.002 - 0.010 | Where the average depth of flow is at ≥ 2 times the height of the vegetation | Supple tree seedlings such as willow or cottonwood growing where the average depth of flow is at ≥ 3 times the height of the vegetation |
| 0.010 - 0.025 | Where the average depth of flow is between 1 - 2 times the height of the vegetation | Moderately dense weeds, or tree seedlings growing where the average depth of flow is from 2 -3 times the height of the vegetation |
| 0.025 - 0.050 | Where the average depth of flow is about equal to the height of the vegetation | 8- to 10-year-old willow or cottonwood trees inter-grown with some weeds and brush (none of the vegetation in foliage) |
| 0.050 - 0.100 | Where the average depth of flow is < 0.5 times height of the vegetation | bushy willow trees about 1 year old inter-grown with weeds along side slopes (all vegetation in full foliage) |
References[edit]
- ↑ Arcement, G.J., Schneider, R. Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains U.S.G.S. WATER-SUPPLY PAPER 2339, 1989 http://eh.sdsu.edu/usgs_report_2339.pdf Accessed Dec 19 2017